9 replies to this topic

[Tornado99]

Have had an older Smiths tachometer on my '88 mini for past 9 months. This is a used, 80 mm(?) Type for electronic ignition cars. Has been very solid until today where it suddenly started fluctuating the needle quite "bigly" while on an extended drive. Checked the black white lead at the coil which feeds to tacho (stock wiring loom) and it seems solidly attached.
Does this sound like a bad connection at the guage or a mechanical issue with it? Could a vacuum leak be giving the EI some issues making it give weird signals to tacho? Engine seems to idle and run just fine.

[sonscar]

Erratic tacho used to be a warning to check your points,,but if you are electronic?Expect a breakdown?.Old electronics could be failing.Have fun,Steve..

[Tornado99]

Previous owner implied the Pertronix Ignitor III EI was only a couple of years old. I did have a coil fail a few months back, replaced with new pertronix Flamethrower unit.

[Spider]

It could be the capacitors in the unit giving up (they do have a finite life) and / or the needle damper needing servicing.

[Tornado99]

Out around town today the tacho was back to normal. Still a mystrey as to cause as I had not touched it since having issue a week ago.

[Tornado99]

Just a follow up on this. The issue still occurs, typically 45+ minutes of driving around. Have noted the metal "pod" casing I have the tacho mounted in, a MiniSpares pod, has become noticeably warm to touch when the needle is fluctuating. Unsure if this is a cause or just normal. There is a standard incandescent bulb in the tacho which is on all the time as I drive around with full lights on for better visibility to other drivers. So perhaps the pod is contributing to excessive heat build up on the tacho electronics. There are no vents in the pod, only the cable exit which is pretty much jammed with the wiring I fitted. 

 

Will try pulling the tacho out of the pod (friction fit) and removing/replacing the illumination bulb with an LED for less heat/better light output. Anyone know off hand what the bulb type is so I can pre-order a replacement?

[I hate Brian]

I think they are 501 type lamps

[beardylondon]

I’ve got the same smiths tachometer and pod on my 66, I have electronic ignition, new one fitted 2 years ago when I refurbed the engine and it still fluctuates badly. I read on the forum ages ago it could be the coil, but haven’t got round to looking in to it.

I never drive with lights on in the day, so have never noticed heat build up.

Edited by beardylondon, 18 December 2021 - 09:27 PM.

[Ol timer]

had a similar problem the other day mine was jumping and the car was bogging down a bit. turned out to be the dizzie cap

[Tornado99]

My issue is unrelated to engine issues, runs fine when tacho twitches. Once it start twitching, seems to persist for rest of the drive, so does seem like a temp build up issue. Always seems fine again on next drive, assuming been switch off for a period of time.